Re: [RFC PATCH] powerpc: udbg: export udbg_putc

On Saturday 13 May 2023 15:53:19 Randy Dunlap wrote:

Hi Pali,

On 5/13/23 02:13, Pali Rohár wrote:

quoted

On Friday 12 May 2023 22:58:04 Randy Dunlap wrote:

quoted

In a randconfig with CONFIG_SERIAL_CPM=m and
CONFIG_PPC_EARLY_DEBUG_CPM=y, there is a build error:
ERROR: modpost: "udbg_putc" [drivers/tty/serial/cpm_uart/cpm_uart.ko] undefined!

The build can be fixed by exporting "udbg_putc" in udbg.c.

OTOH, maybe something like this is more appropriate in
arch/powerpc/Kconfig.debug?

config PPC_EARLY_DEBUG_CPM
	bool "Early serial debugging for Freescale CPM-based serial ports"
-	depends on SERIAL_CPM
+	depends on SERIAL_CPM=y

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <redacted>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Pali Rohár" <pali@kernel.org>
---
 arch/powerpc/kernel/udbg.c |    1 +
 1 file changed, 1 insertion(+)

diff -- a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c

--- a/arch/powerpc/kernel/udbg.c
+++ b/arch/powerpc/kernel/udbg.c

@@ -14,6 +14,7 @@
 #include <asm/udbg.h>
 
 void (*udbg_putc)(char c);
+EXPORT_SYMBOL(udbg_putc);
 void (*udbg_flush)(void);
 int (*udbg_getc)(void);
 int (*udbg_getc_poll)(void);

Hello! I do not think that it is a good idea to export udbg functions
for kernel modules. I have quickly looked at the cpm_uart driver file

Sure, that was just a conversation starter.

quoted

drivers/tty/serial/cpm_uart/cpm_uart_core.c and it looks like that once
udbg from it is registered then there is no code for unregistering it.
So I have feeling that compiling cpm_uart driver as module should not be
allowed when CONFIG_SERIAL_CPM_CONSOLE is enabled, and early debug
should depend on CONFIG_CONSOLE_POLL || CONFIG_SERIAL_CPM_CONSOLE.

The other change above also fixes the build error: (Option 2)

quoted

quoted

config PPC_EARLY_DEBUG_CPM
	bool "Early serial debugging for Freescale CPM-based serial ports"
-	depends on SERIAL_CPM
+	depends on SERIAL_CPM=y

Also, making SERIAL_CPM (cpm_uart driver) be restricted to not allow it
as a module when SERIAL_CPM_CONSOLE is enabled [how does one express that
in Kconfig language?] will cause a circular dependency since SERIAL_CPM_CONSOLE
depends on SERIAL_CPM=y. It looks like you are suggesting reversing the
dependencies.

I see that SERIAL_CPM_CONSOLE has already "depends on SERIAL_CPM=y".
Am I right that this already disallow compiling cpm_uart driver as
module when SERIAL_CPM_CONSOLE is enabled?

quoted

Any other opinion?

Yes, please. Otherwise I prefer my option 2.

-- 
~Randy

Option 2 looks like a better solution.